Towards the end of using self-hosted email at $dayjob, a couple of years ago now, Google started bouncing [some of] our email.
In the header for the bounce messages was included a description of the problem (as they perceived it), and a link for background reading.
I never followed up on it personally (that wasn't my job anymore because reasons), but the bounces seemed descriptive-enough for someone who was paid to care about it to make it work.
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Towards the end of using self-hosted email at $dayjob, a couple of years ago now, Google started bouncing [some of] our email.
In the header for the bounce messages was included a description of the problem (as they perceived it), and a link for background reading.
I never followed up on it personally (that wasn't my job anymore because reasons), but the bounces seemed descriptive-enough for someone who was paid to care about it to make it work.
Was that not the case for you?
That relies on the email actually bouncing. I think it’s more common for it to just silently be filed as spam.